[optimization] traced_selection is used very intensively in debug mode
optimizing it is worth the pain. Basically : don't do stuff unnecessary
when we don't trace anything.
""" CW - nevow/twisted client
:organization: Logilab
:copyright: 2001-2010 LOGILAB S.A. (Paris, FRANCE), license is LGPL v2.
:contact: http://www.logilab.fr/ -- mailto:contact@logilab.fr
:license: GNU Lesser General Public License, v2.1 - http://www.gnu.org/licenses
"""